Peanut seed and pods are susceptible to contamination by aflatoxin (AF), a carcinogenic mycotoxin produced by Aspergillus flavus Links Fr. and A. parasiticus Speare. Efforts to evaluate peanut lines for resistance to AF contamination have been impeded by limitations to the methodologies available for AF detection. AF cannot be seen by visible light and its detection involves grinding seed tissue in organic solvents, separation of phases, and detection by ELISA, high performance liquid chromatography (HPLC) or thin layer chromatography. These methodologies are time-consuming, expensive, labor-intensive, and are uninformative in defining the tissues of the peanut seed and pod that are most frequently contaminated with AF. Aspergillus AF mutants which accumulate norsolorinic acid (NOR), an orange-pigmented AF pathway intermediate, provide an easy and convenient mean to detect AF contamination. A visual rating scheme for NOR contamination of peanut seed was developed that correlated favorably to HPLC detection of both NOR and AF (r = 0.96 and 0.95, respectively). When screening the 38 plant progenies that comprise Tamspan 90 (a spanish cultivar), NOR was first seen in the intercotyledonary cavity and the interfacial surface of cotyledons and testae in seeds examined from infected pods. Immature pods were often heavily contaminated with NOR. Six of the 38 lines accumulated low levels of NOR in two laboratory tests. Additional studies are needed to determine if these results are predictive of aflatoxin contamination under field conditions.
1Contribution from the Texas Agri. Exp. Stn, Texas A&M Univ. System, College Station, TX. This publication was supported in part by the Peanut CRSP, U.S. Agency for International Development, under grant number DAN-4048-G-0041-00. Recommendations do not represent an official position or policy by USAID.